Polyvinyl alcohol emulsion coating



Patented May 2;, recs roLYvrNYi. onoL EMULSlON cosrrnvd Wesley G. howeand Kearney 1. Grlilln, Roche ester, N. Y1, assignors to Eastman KodakCompany, Rochester, N. Jersey No Drawing.

Application September 11, Serial No. 501,990

Y., a corporation of New if Mathis. (Cl. 117-34) This invention involvesa method of preparing photographic products from polyvinyl alcoholsliver halide emulsions.

that by subjecting emulsion layers to those treat- Polyvinyl' alcoholhas beenreierred to as a carrier for the silver halide in photographicemulsions as described, for instances, in U. S. Patents 2,311,058 and2,311,059 of Wesley G.

Lowe. Up to now, in preparing photographicproducts from those emulsions,no method has been developed which assures a rapid setting thereof, suchas is obtained in the coating of gelatin emulsions in which chilling isemployed. The use of various gelling agents with polyvinyl alcoholphotographic emulsions to form a thermal reversible ge'lhas beensuggested and, although setting of the emulsion is obtained by chillingwith those compositions, nevertheless, that setting action isnotsuihciently rapid to compare with the setting obtained when gelatinemulsions are used in the preparation of photographic products.

One object of our invention is to provide a method for the rapid settingof polyvinyl alcohol emulsion layers so that photographic products maybe easily manufactured therefrom with the use of only a reasonableamount of time for that merits a rapid setting of the emulsion layer isobtained resulting in uniformity and ease of preparation of thephotographic product.

We have found that by the incorporation of but a small amount of a boroncompound in a polyvinyl alcohol photographic emulsion at a pH of notmore than 6, the emulsion may be read- 5 ily coated out upon a supportsuch as. paper or iilm base to form a thin layer which is quickly set byfuming with ammonia or the like.

' Anyone interested in the processwhich we have found might consider theuse of ammonia on a operation. Another object of our invention is toprovide a method for preparing photographic products from polyvinylalcohol emulsions in which the emulsion may be coated out at ordinarytemperature. A further object of our invention is to provide a methodforsetting polyw vinyl alcohol photographic emulsions which method isnot affected by the presence oi gelatin in the emulsion. Many of thejelling agents previously proposed lose their effectiveness whenphotographic emulsion as undesirable because it is known to increase thegraininess and speed of emulsions and to raise their pH. We have found,however, that by our process in which the ammonia issupplied by fuming,there is no appreciable increase of either graininess or speed in thepolyvinylalcohol photographic emulsion and that the drying operationwhich is "employed to dry the'emulsion layer alsordrives off any ammoniawhich may be present in the emulsion and a pH of 7' isfinally' obtained.

Various boron compounds have been. found to be' suitable. For instance,borer, sodium borate, boric acid, or the like may be employed providingit is mixed with the polyvinyl alcohol emulsionunder acid conditions.The phi or"; the

emulsion should never beallowed to exceed 7 and it is preferably kept ata pH of not-more than ii.

Although our setting method is not of any particular value forsetting anemulsion en masse,

- it is of very great value in the preparationfof gelatin is employedwith polyvinyl alcohol in photographic emulsions. This disadvantage isplates, films or paper involving the coating out of polyvinyl alcoholemulsion thereon. Durin this step in the process of manufacturing light,

' sensitive photographic products, it is'necess'ary to avoided by ourinvention. A still further object of our invention is to provide amethod for costing out polyvinyl alcohol emulsions in which lowviscosity polyvinyl alcohols have been employed in their preparation.Due to the nature of our invention, low viscosity or greatly dilutedpolyvinyl alcohol solutions can be employed without.

being washed away such as in some processes where contact with liquid isinvolved. Other 0b:- 7

jects will appear herein.

get very rapid setting to avoid flow of the emulsion on the film orpaper, the necessity being greater in the caseof film because suchcoatings fare often appreciably thickerthan coatings on Our inventioninvolves the preparation of photographic products using polyvinylalcohol emulsions in which setting is accomplished. by

incorporating boron compounds into the emulsion composition and, aftercoatlngout the emulsion onto its support, fuming of the emulsion layerwith a volatile base such as ammonl methylamine or ethylamine. We have"I paper thus tending to causeiiow inspite of the viscosity inherent inthe emulsions. r

.We have found that only very smallrproportions of boric acid or acidsolutlon'of borax are necessary in the, emulsion in order to obtainrapid setting of polyvinyl alcohol photographic emulsion layers byfuming the emulsions with ammonia. We have found that ordinarily 1% oreven less of boric acid (based on the weight of polyvinyl alcohol)is'suflicient to accomplish the desired result and that any proportionbetween 1 and 6% based on the weight of the polyvinyl alcohol willaccomplishthe purpose desired; Al-

found though the use of a. greater proportion than 6% instance, coatingsup to .005"

of boric acid may be employed, it is known that larger proportions ofboron compounds exert marked effects on the viscosity of polyvinylalcohol and too great a proportion of boron compound does increase thedifficulties in the coating operations. Where, however, this is notobjectionable, such as where the emulsion is warmed immediately prior toapplying as an emulsion layer, there is no objection to the use oflarger.

such as by passing the film immediately after coating through a fumingbox saturated with ammonia gas. If the emulsion layers are too thick,the setting action is not as rapid as with the ordinary thickness ofemulsion layer. For are satisfactorily set by a very short fumingoperation, whereas coatings much in excess of .005" require a littletime of fuming before those coatings are sufiiciently hard to withstandfurther processing of the emulsion layer,

Our method of setting photographic emulsion layers makes possible theuse of very low viscosity polyvinyl alcohols as the carrier for silverhalides. Our invention makes possible more dilution of polyvinyl alcoholphotographic emulsions than has been considered safe previously toassure a uniform and substantially even coating. A very convenient wayto prepare photographic products in accordance with our invention is tofirst treat the polyvinyl alcohol emulsion with a gelling agent so as togel the same at a low temperature thereby enabling the operator to cutthe emulsion into shreds and wash the same. Thereupon the shreds arewashed with cold water to remove everything but the silver halide andthe carrier therefor. The washed emulsion may then be worked up andemployed by coating it out on photographic film or photographic paper.For instance, a good photographic paper may be prepared by taking anordinary baryta coated paper,

particularly one which has been coated with a polyvinyl alcohol inbaryta as described and claimed in Clark application Serial No. 348,013,and applying a coating thereto of a polyvinyl alcohol emulsioncontaining borax therein. After the coating operation has beencompleted, the emulsion layer is at once subjected to the action ofammonia gas which sets the emulsion enabling it to be readily driedwithout any waviness or other irregularity therein.

The following examples illustrate our invention:

- Example 1 An emulsion of silver halide-polyvinyl alcohol was preparedcontaining a-naphthol therein in accordance with the directions given inU. S. Patent 2,311,058. The emulsion was set by gelling, shredded andwashed in accordance with the description of that patent. The emulsionwas then warmed to liquefy it, the pH was adjusted to 5 and 100 cc.thereof was mixed with 2 cc. of

. act as the vehicle for the were free from fog. It is to be understoodthat the preparation and refining of the emulsion was all carried outunder darkened conditions.

Example 2 A portion of the emulsion of Example 1 containing acidifiedborax was diluted with 5 its weight of water. This lowered its viscosityand made coating easier. The emulsion was then coated out on a glassplate and fumed with ammonia as before. The emulsion set very rapidlyand the resulting product gave good sensitometric results.

Example 3 Some of the emulsion, as prepared in Example 1, was coatedonto a cellulose acetate film base which was then passed through achamber filled with ammonia gas. Very rapid setting occurred and thefilm was readily dried in a stream of air in the usual way. In this casethe thickness of the coating was of the order used on commercialphotographic film. Examination of the developed image obtained with thefilm showed that it was not higher in graininess than the developedimage from the same emulsion not fumed with ammonia. The photographicspeeds were also equal whether or not ammonia was used to set theemulsion.

Example 4 A silver halide emulsion .was prepared by first preparing thesilver halide in a solution containing gelatin as the silver halidedispersing agent followed by the addition of polyvinyl alcohol to silverhalide as described in U. s, Patent No. 2,276,323 of Wesley G. Lowe. Theratio of gelatin to polyvinyl alcohol in the emulsion was about one toten. cc. of the emulsion was taken and its pH was adjusted to 5.5 by theaddition of acetic acid. 2 cc. of 4% acid boric solution (pH 6) wasadded thereto and the emulsion was coated on film base. Fuming withammonia gave rapid setting and the dried and processed film showed noincrease in graininess due to the action of the ammonia.

Example 5 A silver halide emulsion was prepared by preparing the silverhalide as in the preceding exampreceding example and in the samequantity. The emulsion was coated onto film base and fumed with ammonia.It was found that rapid setting occurred and that the film dried andcould be processed in the usual manner.

It is to be understood that in each of the exthe polyvinyl alcoholpredominates. For instance, even the ordinary commercial polyvinylalcohol has only been hydrolyzed to a point where it still containsapproximately 1 to 5% of polyvinyl acetate. If, however, the hydrolysishas beencarried out to a point sufiicient to give the material thecharacteristics of polyvinyl alcohol that hydrolyzed material comesunder the polyvinyl alcohol designation which is employed herein.Ordinarily this would mean at least 50% of polyvinyl alcohol present inthe material employed as the carrier for the silver halide in thephotographic emulsion.

Our invention is directed to a process of setting photographic emulsioncoatings, and admits of reversing the setting characteristics if, forany reason, the operator desires to again liquefy the emulsion. Forinstance, after a photographic product has been prepared, if testing ofthat product does not show the desired properties, the emulsion may berecovered by treatment with, aqueous acid such as by soaking thephotographic product in a dilute solution of acetic acid for a time.After recovering the emulsion from its support in liquid form, it may befurther treated and again coated out on a support such as a glass plate,photographic paper or film base and fumed with a volatile base to againcause setting.

We claim:

1. A method of preparing photographic products from polyvinylalcohol-silver halide emulsions which comprises incorporating a smallproportion of boric acid in the emulsion at a pH of not more than 6,coating out the emulsion upon a support, fuming with a volatile base toset the emulsion, coating and drying the same, all under conditionswhereby the light sensitiveness of the emulsion is not detrimentallyaffected.

2. A method of preparing photographic products which comprisesincorporating in a polyvinyl alcohol photographic emulsion a smallamount of a gelling agent and gelling the emulsion at low temperature,cutting the emulsion into shreds and washing the same, incorporating inthe emulsion a small proportion of an aqueous solution of borax having apH of 6 imparted thereto by acetic acid, coating out the emulsion upon asupport, fuming with a volatile base to set the emulsion coating andthen drying the same all under conditions whereby the lightsensitivenessof the emulsion is not detrimentally affected.

3. A method of preparing photographic products from polyvinylalcohol-silver halide emulsions, which comprises incorporating a smallproportion of a boron compound which forms boric acid under aqueous acidconditions, in the emulsion at a pH of not more than 6, coating out theemulsion upon a support, fuming the emulsion coating with a volatilebase to set the same, and then drying the emulsion coating, all underconditions whereby the light-sensitiveness of the emulsion is notdetrimentally affected.

4. A method of preparing photographic products which comprisesincorporating into a silver halide-polyvinyl alcohol photographicemulsion in aqueous form a small proportion of a boron compound whichforms boric acid under aqueous acid conditions, at a pH of not more than6, coating out the emulsion upon a support therefor, setting theemulsion coating by subjecting to the action of ammonia gas, and dryingthe emulsion coating upon the support, all under conditions whereby thelight sensitiveness of the emulsion is not detrimentally affected.

5'. A method of preparing photographic products from polyvinylalcohol-silver halide emulsions, which comprises incorporating therein asmall proportion of a boron compound, which forms boric acid underaqueous acid conditions, at a pH of not more than 6, coating out theemulsion upon paper, setting the emulsion by fuming with a volatilebase, and then drying the same, all under conditions whereby thelight-sensitiveness of the emulsion is not detrimentally affected.

6. A method of preparing photographic products from polyvinylalcohol-silver halide emulsions which comprises incorporating a smallproportion of borax in the emulsion at a pH of? not more than 6, coatingout the emulsion upon a support, fuming the emulsion coating with avolatile base to set the same and then drying the emulsion coating, allunder conditions whereby the light-sensitiveness of the emulsion is notdetrimentally affected.

'7. A method of preparing ucts from polyvinyl alcohol-silver halideemulsions, which comprises incorporating in the emulsion a smallproportion of borax having a pH of 6 imparted thereto by acetic acid,coating out the emulsion upon a support, fuming the emulsion coatingwith a volatile base to set the same and then drying the emulsioncoating, all under conditions whereby the light-sensitiveness of theemulsion is not detrimentally affected.

WESLEY G. LOWE. KEARNEY P. GRIFFIN.

photographic prod-

